The objectives of the proposed research are to investigate events involved in the regulation of cell nuclei during mammalian spermatogenesis, in the initiation of DNA synthesis in the mammalian sperm nucleus in vitro, and in the formation of the male pronucleus during fertilization. Proposed experiments are designed to: (1) determine the factors involved in nuclear decondensation and release of template restrictions for DNA synthesis in vitro in the spermatozoa of a variety of mammalian species; (2) determine factors involved in vitro and in situ in regulating DNA template activity during spermatogenesis; (3) determine temporal relationships between protamine replacement by histones, disulfide bond reduction, nuclear decondensation and release of DNA template restrictions in the fertilizing spermatozoon; (4) determine from in situ studies of fertilization the roles of endogenous sperm nuclear factors and egg cytoplasmic factors in the formation of the male pronucleus. The results obtained from these experiments should increase our understanding of the regulation of chromatin condensation and regulation during spermatogenesis, and chromatin decondensation and activation during fertilization.